Computer



Oct. 13, 1959 R. G. PIETY 2,908,889

' COMPUTER Filed Dec. 16. 1955 1s Sheets-Sheet 1 INVENTOR.

R. G PIETY ATTORNEYS R. G. PlETY COMPUTER l6 Sheets-Sheet 2 Filed Dec. l6. 1955 FIG. 2a

l5 "20 TIME INVENTOR. R.G. PIETY FIG. 2a

M l A ORNEYS R. G. PlETY COMPUTER File d Dec. 16. 1955 16 Sheets-Sheet 3 INVENTOR.

R.G.PIETY ATTORNEYS R. G. PIETY Oct. 13, 1959 COMPUTER Filed Dec. 16. 1955 16 Sheets-Sheet 4 FIG 4 O m /w II A DDDDD) :1 m m 3 w INVENTOR. R G PIETY ATTORNEYS FIG. 7

Oct. 13, 1959 R. G. PIETY 2,908,889

COMPUTER Filed Dec. 16. 1955 16 Sheets-Sheet 6 INVENTOR. R.G. PIETY ATTORNEYS Oct. 13, 1959 R. G. PIETY 2,908,889

COMPUTER Filed Dec. 16. 1955 16 Sheets-Sheet 7 ATTORNEYS Oct. 13, 1959 R. G. PIETY 2,908,889

COMPUTER Filed Dec. 16. 1955 16 Sheets-Sheet a FICA/2b FIG. /2a

INVENTOR. R. G. Pu: TY

AT TOR NEYS R. G. PIETY COMPUTER 16 Sheets-Sheet 10 Filed Dec. 16. 1955 mmh zu 5mm 86$ "A S ow muQmOUum snow mmN

INVENTOR. R G PIETY ATTORNEYS R. G. PlETY Oct. 13, 1959 COMPUTER l6 Sheets-Sheet 11 Filed Dec. 16. 1955 INSTRUMENT RESPONSE TRUE LOG INTENSITY RECORDER FIG. I51:

INVENTOR. R G PIETY ATTORNEYS D'EPTH Oct. 13, 1959 Filed Dec. 16.

R. e. PIETY 2,908,889

COMPUTER 1e Sheets-Sheet 12 MEASURED LOG INTENSITY I I I I I 220 INVENTQR. R.G.P|ETY ATTORNEYS 08. 13,1959 R. G. PIETY 2,908,889

COMPUTER Filed Dec. 16. 1955 16 Sheets-Sheet 13 FIG. /6,

FIG. IZ INVENTOR. R.G. PIETY AT TORN EYS .R. G. PIETY 2,908,889

COMPUTER 1e Sheets-Sheet 14 Oct. 13, 1959 Filed pee. 16. 1955 1959 R. G. PlETY v 2,908,889

' COMPUTER Filed Dec. 16. 1955 7 l6 Sheets-Sheet 15 INVENTOR. R.G. PIETY BYHM'JAM ATTORNEYS' United States Patent COMPUTER Raymond G. Piety, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application December 16, 1955, Serial No. 553,626

48 Claims. (Cl. 340-15) This invention relates to a method of and apparatus for multiplying and/ or dividing algebraic polynomials. In another aspect it relates to a universal tuningsystem. In another aspect it relates to a tuning system for seismograph signals which can be tuned to detect a particular wave form. In still another aspect it relates to a system for obtaining true parameters from measured well logging data. i

This application is a continuation-in-part of copending applications Serial. No. 378,541, filed September 4, 1953, and Serial No. 496,491,'filed March 24, 1955.

In various fields of physical measurement and analysis the data under consideration can be expressed in the general form of an algebraic polynomial of the type a +a x+a x +a,,x"

where the coefficients a a a a represent the magnitude of the individual quantities under consideration and the quantities x, x x represent time, space or the like at which the respective coefiicients a a a are obtained with respect to a reference point associated with the coeificient n The exponents attached to the several In accordance with the present invention, a system is provided for representing mathematical data in the form of algebraic polynomials and for performing basic mathematical operations on such polynomials, that is, the multiplication and division of one polynomial by another. This general procedure belongs to the theory of linear transformations or linear operations, and an operational calculus can be set up to describe such a system. By the use of an operational calculus certain mathematical operations or functions are carried out by first transforming the function, then operatingwith the corresponding operators and finally returning to the original domain by the inverse transformation. The first step is to establish a suitable transformation and the second step is to establish a table of functions and their operational transforms. In ex plaining such an operation it will be assumed that T represents an operation on a function f(z) which converts xs serve to identify the time, space or the like at which the respective coeflicients are taken. For example, an

electrical voltage sine wave of 1r period and unit maximum value can be expressed as follows:

wherein the coeflicients 0.7, 1.0, 0.7, 0, 0.7, -l.0, 0.7

and 0 represent the magnitude of voltage values at respective phase angles of vr/S, 7r/4, 31r/8, 1r/2, 51r/8, '31r/4, 71r/ 8 and 1: which in turn are represented by the respective quantities x, x x x x x x and x By increasing the number of x values within the period 1: the sine curve can be expressed to any desired degree of accuracy. Obviously any other mathematical curve, the magnitude of which varies with time, can be expressed in like manner. An example wherein a physically measured quantity varies with respect to displacement occurs in well logging wherein a sonde is lowered into-a bore hole to measure some property of the surrounding earth formations. In order to interpret such data the measured quantity obtained from the sonde normally is recorded as a function of the depth at which the sonde is lowered. Such a record can be expressed mathematically, for example, as follows:

where the coefficients 1.0, 2.5, 2.0, 2.6, 3.0 1.7 represent the measured magnitude of the selected property at uniformly increasing depths representedby the respective quantities x, x x x x. These twoexamples are illustrative of the fact that any information which can be expressed in the form of a mathematical curve can also be expressed as an algebraic polynomial, the degree of accuracy of such expression being limited only by the it into a new function r( k). This is expressed as T f(z) The theory advanced herein is concerned with operators that satisfy the following conditions or postulates:

where the pairs, f and r and r in (6) satisfy (5). Conditions (5) and (6) are referred to the linearity requirements and condition (7) makes the operator an operator of the closed cycle.

In many systems of physical measurement the desired functions are empirical because they normally are obtained from reading graphs or meter scales. In order to apply the theory herein developed to the interpretation of measurements made on a physical system, it must be postulated that when a physical parameter specified by a set of numbers z determines another parameter given by the numbers J(z) then the set of numbers given by the instrument or measuring system r(x) must satisfy conditions (5), (6) and (7). For example, if f(z) specifies the gamma ray intensity of horizontal beds penetrated by a vertical bore hole, z specifies the distance to the beds from some reference point and r(x) specifies the measured gamma ray log, then to apply the theory it must be true that beds with k times the gamma ray intensity will produce k times the instrument response. This is condition (5) or a law of behavior that the measuring system must satisfy to 'be represented by the mathematical model herein defined. Furthermore, a system of beds that has a gamma ray intensity (z) which is the sum of the intensities of two separate systems 71(2) and f (z) will produce an instrument response r(k) which is the sum of the instrument responses of f (z) and M2) or tion (7) is almost always satisfied in a physical system under measurement. This latter condition is to the eifect that if the original or zero reference point is shifted then the zero reference of the response is shifted by the'same amount. Whenever differential equations are considered and z represents time, condition 6) means, amongother things, that the differential equations have constant coeflicients. In theabove example wherein 2 represents a number of values selected within the range of the curve.

spacecoordinate such as a well depth, the corresponding meaning is that the basic behavior of the logginginstru- .ment is a function only of the relative position of the instrument in the well.

Pat nted Oct. 13, 1959 As employed herein the symbol G before f(z indicates the operation of forming u(2 c such that valuesmust be selected by some rule. I I The operator G is a linear-operator for If f(z) is defined for values other thana thenthe othe r as can be seen by carrying out the operations designated.

Ifh in(7) is the'tabular interval or an integral multiplethereof, then Gis an operator ofthe closed cycle is a correspondence between the input signal and the desired signal'the measured product becomes a maximum I which is indicative of the correspondence.

One-particular example of the use of the computing system of this invention to divide algebraic polynomials occurs in'interpreting well logging data. In the case of well logging an instrument is lowered into the bore hole which is sensitive to some physical property (parameter) of the materials surrounding the instrument. At any position inthe hole theinstrument has an output WlIllCll is I a Weighted average of the value of the parameter through-.

out a region surrounding the instrument. The weight factor is-assumed to 'be a geometrical factor which assumes the same value for all points on a circle centered on the axis of the hole and lying in a plane normal to that axis. In general, the weight factor falls ofi to negligiblevaluesbeyond a few feet from the instrument. As

. the instrument is lowered in the hole this zone ofinfluence may be thought of as moving with the instrument and scanning the hole. The instrument output therefore, a running weighted average which prevents the 10g from having a point to point correspondence with a parameter characterizing the formations penetrated. The nature of this scanning or integrating process is an important property of the log and may be used to characterize the basic complexity of the method of measuring the. parameter. If the instrument response to a certain From (14) the G transform ofthe'first difierence A is i The G transform for'the nth difference ten as Equation 14- is of considerable importance in that it interprets the meaning of the indeterminate x in the polynomial of EquationS. 'F'rom the fact thatthe product I of two polynomials Q(x) and P(x) can be written Q-(r)' al Q( )a1 +Q( 2 +L- 4 7) the resultantpolynomial can be thought of as composed maybe writa.

. individual .bed, is-known, the true parameter of the, bore hole can be'obtained by dividing the measured response by the instrument response to a single bed. I

' Acccor-ding, it it is an object of this invention to provide an improved method of and apparatus for multiplying and dividing algebraic polynomials.

I Another object is to provide a universal tuning system which is adapted to detect wave forms of any predetermined configur-ation surveying whichcan be tuned to transmit a predetermined waveform.

. Still another object is to provide a system for obtaining true parameters from measuredwell logging data.

ofpolynomials. Q(x)1' 'weighted according to the values .of'P(x).' operation.

The computing system of this invention is particularly adapted for use as, a'universal tuning system. By.a

This is generally referred to as a convolution universal tuning. system isme'ant a system which can be tuned torespond to a wide class of signal spectra. Such a system is of importance in seismic prospecting, for example. Seismic prospecting, as is well known by those skilled in'the art, is a system whereby information is obtained regarding subsurface earth strata by transmitting vibrations from a first preselected point at or near the I surface of theearth downward to theformationsland Trneasuring the reflected or refracted vibrationsat other pick-up locationspositionedat or near the; surface of the earth. To this end. an explosive charge is detonated in a shot hole and a plurality of vibration picleups are disposed in a'preselectedpath spaced from the shot' hol e. The vibrations incident upon these picl t-ups are converted into corresponding electrical signals which normally are amplified and recorded in relation to one;another.: By timing the arrival of selected reflections valuable infor l mation can be obtained regardingthe depthland slope of selected earth formations. Unfortunately, extraneous vibrations usually are present which tend to obscure the recognition oflthe desired signals. Thus, it isdesired resentative of undesired Treflectio ns or stray vibrations expression representative of the signal whichis desired to be transmitted by the tuning system. Whenever there .to be able to tune the vibration pickup mechanismgso as i i to eliminate the high or low frequencies which are rep- Various other objects, advantages and features of this invention should become apparent from thefollowing detailed description taken in conjunction with the accompanying drawing in which: I V I Figure I is a'schematic representation of seismic exploration apparatus; I 1 I e Figures Za and 2b are. simplified representations of seismic signals recorded by the apparatus of Figure 11; Figureslc and 2d are representations of transformed signals obtained 'inflaccordance with this invention;

Figure 3. is a schematic view of a first embodiment of the polynomial multiplying apparatus employed to inter 'pret. seismic data; I Figure 4'is a view taken along line '44 in Figure 3;

Figures 5, 6; and 7 are schematic circuit diagrams of weighted amplifiers utilized in the computing mechanism;

Figure 8 is a schematic view of a second embodiment of the polynomial multiplying apparatus employed to in- :terpret seismic data;

Figure 9.7is a second view of the apparatus of Figure 8;

f ig res 8 and 9; g re 11 is a modifiedform ures 9 and 10;.- 1 r T "Figure IOis a schematicsectional view of the apparatus I of the 'apparatus of Fig- Figures'lZa and 12b illustrate anembodiment of polynomial multiplying {apparatus indisassembled position; Figures 13a-and 13b illustrate in-a schematicmanner .electrical .circuit' details of .thefappar'atus. of Figures .12a

and 1263 1., 7 p

. Figure 14 is a schematic view of oneembodiment of ithepolynomialdividing apparatlis; at I .Figure 15a. is. a'schematic' representation of electrical Welllogging apparatus; 7

Figures 15b; 15c anaisd illustrate an application of Another object is to provide a filter system for seismic '5 the computing mechanism of this invention to the interpretation of well logging data; v p

Figure 16 is a schematic representation of the mechanical components of another embodiment of the signal transforming apparatus;

Figure 17 is a detailed view of a portion of the signal storage apparatus of Figure 16 in disassembled relation;

Figure 18 is a schematic circuit diagram of a first embodiment of the electrical components of the signal transforming apparatus of Figure 16;

Figure 19 is a schematic circuit diagram of an amplifier employed in Figure 18;

Figure 20 is a schematic circuit diagram of a modification of the apparatus of Figure 18; i a Figure 21 is a schematic view of a magnetic sign storage unit; and

' Figure 22 is a schematic diagram of an embodiment of this invention employing electrical delay lines.

In order to describe the operation of this invention as an algebraic polynomial multiplier, reference is made herein to a specific application involving the recognition of selected reflections in seismic surveying. In Figure 1 I there is illustrated a simplified conventional seismic surveying system. An explosive charge is positioned within a shot hole 11 and electrically connected to a detonator 12 positioned at the surface. Detonation of explosive charge 10 results in vibrations being transmitted outward therefrom in'all directions. .A plurality of vibration'pickup seismometers 13, 14, 15', 16 and 17 is positioned at or near the surface in a predetermined geometric array. In the illustrated example, vibrational waves travel downward from explosive charge 10 and are reflected upward from bed 19 to the several seismometers 13-17. It should be apparent from the figure that these reflected waves arrive atthe five seismometers at slightly different times. seismometer 13 is actuated first and there is a short time delay between arrivals of the reflected waves at seismometers 14, 15, 16 and 17. This difference in time between actuation of the several seismometers is due to the difference inthe length of paths traveled by the several reflectedwaves downward from charge 10 to bed 19 and back upward to the surface. This time interval is, therefore, a definite function of the depth and dip of bed 19 and the geometric arrangement of the several seismometers at the surface. By measuring the time of arrival of the reflected signals at the different seismometers, the depth and dip of bed 19 can be determined if the velocities of the seismic waves in the various formations between the surface and bed 19 are known.

For purposes of determining the time of arrival of the reflected waves at the several seismometers it is conventional to record the vibrations picked up at these seismometers by suitable electrical equipment which conven iently is carried in a truck 21. By recording the vibrations from the several seismometers side by side on a common recording medium, it is sometimes possible to obtain the time of arrival of the reflected waves by direct observation of the recorded traces. In Figure 2a there is illustrated a somewhat ideal record of such recorded vibrations at a single seismometer, wherein the output voltage of the seismometer is plotted against time. The vibration pattern illustrated between the time intervals and 1 represents the wave reflected from bed l9.

As is well known, surface waves, refracted waves and other more or less random waves are generated by the detonation of explosive 10. In actual practice the prob lem of identifying a reflected signal such as shownin Figure 2a is complicated by the fact that othe'r vibrations of varying amplitude and frequency usually are received at the seismometers in addition to the desired reflected signal. These latter waves are of course received by the several seismometers 13 17 and aresuperimposed on the desired reflectedwave. In Figure 2b there is illustrated a curve which approximates the vibration actually received does the curve illustrated in Figure 2a. However, even the curve of Figure 2b is idealized to a certain extent, and in actual practice even more stray vibrations generally are superimposed upon the desired reflected signal. The presence of these stray vibrations obviously tends to complicate the problem of distinguishing the reflected waves and particularly determining the exact time of arrival of the reflected waves.

In order to provide a tuning system which recognizes the desired reflected wave form, the computing system of the present invention is employed. One particular embodiment of apparatus in accordance with this invention is illustrated in Figures 3 and 4. The output signals from seismometers 13, 14, 15, 16 and 17 are applied to the input terminals of respective amplifiers 23, 24, 25, 26 and 27. The output terminals of amplifiers 23, 24, '25, 26 and 27 are applied to respective magnetic recorders 30, 31, 32, 33 and 34 which are positioned above and in closely spaced relation with respective annular strips of magnetic material 35, 36, 37, 38 and 39, the latter being mounted on the upper surface of a disc 40 which is rotated at a predetermined speed by a motor 47. Magnetic recorders 30, 31, 32, 33 and 34 are positioned along a radial line of disc 40 and can be of any conventional structure known in the art which is adapted to magnetize the adjacent magnetic strips when an electric current is applied to the recorder. Thus, the output electrical signals from seismometers 13, 14, 15, 16 and 17, which are representative of the vibrations received by these seismometers, result in respective strips 35, 36, 37, 38 and 39 being magnetized in accordance with the vibrations received by the respective seismometers. Disc 40 is rotated in a counterclockwise direction as illustrated in Figure 3 such that continuous records of the seismometer outputs are applied to the respective magnetic strips, A series of five obliterating units 41, 42, 43, 44 and 45 is positioned above disc 40 adjacent respective recorders 30, 31, 32, 33 and 34 such that the individual units are located in closely spaced relation to respective strips 35, 36, 37, 38 and 39. A source of high frequency voltage 46 is connected in circuit with each' of the obliterating units to demagnetize the individual strips continuously as disc 40 is rotated. Thus, any magnetism induced in the individual strips by the recorders is erased before the strips pass back under the respective recorders. A plurality of pickup units, which can be of construction similar to the magnetic recorders, is disposed above and in closely spaced relation with each of the strips 35, 36, 37, 38 and 39. In the illustrated embodiment there are fourteen pickups associated with each magnetic strip. Pickups 50a, 50b, 5011 are positioned abovestrip 35 in equally spaced relationship; pickups 51a, 51b,

51n are positioned above strip 36 in equally spaced relationship; pickups 52a, 52b, 5211 are positioned above strip 37 in equally spaced relationship; pickups 53a, 53b, 5311 are positioned above strip 38 in equally spaced relationship; and pickups 54a, 54b, 5411 are positioned above strip 39 in equally spaced relationship. As the individual magnetic strips pass under the respective pickups associated therewith, voltages are induced in the pickups which correspond to the voltages previously applied to the respective magnetic recorders from the seismometer amplifiers 23-27. The output terminals of {pickups 50a, 50b, 5011 are applied to the inputterminals of respective amplifiers 70a, 70b, 7011; and the output terminals of pickups 54a, 54b, 54n are applied to the input terminals ofrespective amplifiers 74a, 74b, 7411. The amplifiers connected to pickups 50c, 50d, 50m and to pickup coils 54c, 54d, 54m are omitted from Figure 3 for purposes of simplicity. In like manner corresponding amplifiers are connected to the pickups 51a, 51b, 51n;'52a, 52b, 5211f;

' and 53a, 53b, 53n, but these latter amplifiers also are omitted from the drawing for pru'poses of simplicity.

by any one of the seismometers tolacloser degree than 75 The output terminals of amplifiers 70a, 70b, 70n

rm example. 1

are connected across the endterminals of respective po= Potentiometers 75a,

74b, 7411 are connected across the end terminals of respective Potentiometers 7901,7911, 79n. Potentiometers 79a, 79b, L .7911 are likewise provided with grounded center taps. The output contactors of poten- 8 triode 126 is connected to age source 131 through an anode'resistor 132and the anode of triode 128 is connected to the positive terminal of voltage source 131 through an anode resistor 133. The negative terminal of voltage source 131 is grounded.

. The anode of triode 126 also is connected to thefirst end tiometers'75a,'75b, 75!: are connected through respective resistors 80a, 80b, 80nto the first input terminal of a summing amplifier 86, the second inpnt'terminal of which is grounded. The output terminals of amplifier 86 are applied to the first set of input terminals of a multichannel recorder 87 which provides a trace 88 on a chart 89, the latter being moved past recorder 87 at a predetermined speed. Recorder 87can be any type recorder desired. The output contactors of potentiometers 79a, 79b, 7911 are connected through respective resistors 84a, 84b, 8411 to the first input terminal of a summing amplifier 90, the second input ter: minal of which is grounded. The output terminals of amplifier 90 are applied to a second set'of input terminals of recorder 87 which provides a second trace 91 on chart 89. Three other traces 92, 93, and 94 are provided on chart 89 by the summing amplifiers, not shown, which are employed to sum the outputs of the amplifiers connected to the respective pickups 51a, 51b, 51; 52a,

52b, 5211; and 53a, 53b, 5311. The amplifier and summing circuits associated with. these latter groups 'of pickups are identical to the circuits illustrated, but are omitted from the drawing for;the purpose of simplicity. In Figures 5, 6, and 7 three amplifiers are shown which wave form is as illustrated in Figure 2a between time can be employed as amplifiers 70a; 70b, 70n or 7 74a, 74b, 74n in Figure 3. In the amplifier illustrated in Figure 5, a first input terminal 100 is connected to the control grid of a vacuum tube triode 101 and the second input terminal 102 'is grounded. 'The anode of j triode 101 is connected'to the. positive terminal of a voltage source 103 through an anode resistor 104 and the cathode of triode 101' is connected to the grounded .negative terminal of voltage source 103 through a cathode resistor 1 05. The anode of triode 101 also is connected to the first end terminal of a potentiometer 107 through a capacitor 108 and the cathode of triode 101 is terminal 113 is connected to the control grid of a first vacuum'tube triode 114, and a second input terminal 115 is connected. to the control, grid of a second vacuum tube triode 116. The cathode of'triode 114is connected to ground through a cathode resistor 117 and the cathode of triode 116 is connected to ground through a cathode resistor 118. The anodes of both triodes 1'14 and 116 are connected to the positive terminal of a voltagesource 120, the negative terminal of which is grounded; The cathode of triode 114 is connected to the first end terminal of a potentiometer 1 21 and-the cathode of triode 116 is' connected to the second end terminal of potentiorrv eter121. Potentiometer 121 is providedvvith ajfirst grounded center tap 122 and with an output 'cQntactor terminal 123 Potentiometerlll also corresponds 'to the output potentiometer a, associated with aniplifienflthz,

' The amplifieriillustrated Figure 7 is provided ;vvit-ha first input terminal 125 which is connected to the control gridof a. first vacuum tube triode 126, the second input terminal 127 being grounded. The cathode of triode 126 is connected to the cathode of a second, vacuum tube triode 128,- and the two cathodes are connectedto ground .througlra comrnon cathode resistor 129. The anode'of terminal of a potentiometer 134 and the anode of triode 128 is connected to the second end terminal of potentiometer 134. Potentiometer. 134 is provided with a grounded center tap 135. The output contactor 136 of potentiometer 134 is connectedthrough a capacitor 138 to an output terminal 139. The junction between capacitor 138 and output terminal 139 is connected to ground through a resistor 140. Potentiometer 134 also corresponds to the potentiometer 75a associated'with amplifier 70a, for

example. i

The operation of the mechanism thus far described to detect the time of arrival of the desired vibration reflections from bed 19 at seismometers 13, 14, 15, 16 and 17 is as follows: One or more preliminary shots are first fired in order to establish the basic form of the reflected Wave to be recognized Normally a location can readily .be found wherein the recorded traces from the seismometers are sutfiiciently free from external vibrations that the re flected wave pattern can be obtained fairlyaccurately, at least from a plurality of trial shots. In making these trial shots conventional recording mechanism is employed, that is, the outputs of seismometers 13, 14,15, 16 and 17 are amplified and recorded directly. For purposes of discussion it will be assumed that the desired reflected intervals t 'and 1 This desired wave form is divided, along the abscissainto as many equally spaced points (fourteen, for example) as pickup coils areprovided above each of the strips on disc 40. In order to simplify the discussion, only seismonieter 17 will be considered. The values of the ordinates of the curve of Figure 2a at each selected time interval are set on the respective potentiometer-s 7911, 79m, 79a. the ordinateof the curve has "a value of +1, at time the ordinate has a value of zero, and at time the ordinate has a value of zero. These ordinate values are establisheicl on the corresponding potentiometers in the 7 conventional manner for multiplication. For example,

let itarbitrarily be assumed that the positive end terminal of potentiometer 79n-is maintained at +5 volts and the negative terminal of potentiometer 7911' is maintained at '5 volts In order to establish a' value of +1 'onpotentiometer 79a, the contactor thereof is positioned at one-fifth the distance between the grounded center tap 1 and the positive end terminal, whereby the voltage at the contactor, taken with respect to ground, is '+1 volt. If the voltage at the positive terminal of potentiometer 79n should increase to +25 volts, then the voltage at the contactor also is increased by a factor offive'to +5 volts.

Once the ordinate'valuesof the curve illustrated in,

Figure Zr zare set on potentiometers 7911, 79m, 79a, the mechanism is ready for operation. 'Seismometer 17 is positioned at the desired location, explosive charge 10 is detonated, and disk 40 is rotated at 'a speed suchthat one complete revolution is made during the interval represented between times 23 and t in Figure 2a. It should be apparent that the vibrations received at seismometer 17 are recorded continuously on strip 39 as disc '40=rotates past magnetic recorder 34; For purposes of discussion it willbe assumed that a vibration pattern exact ly as illustrated; by thecurve of Figure 2b is receivedby seismometer 17L Initially .at zero time a zero voltage correspondingto the-zero ordinate of the curve of Figure 2b lSZEtPPllGd to magnetic recorder 34 which magnetizes the portion of strip 39 then under recorder 34 to a value corresponding'to zeroni'agnitude. It is assumed that i magnetic strip 39 is initially 'de-magnetized such that zero outputs are received at the various pickupcoils 54a,

the positive terminal of a volt- Thus at time 

